Methods and apparatus for uplink control transmit diversity

Abstract

A method and apparatus in a user equipment transmit a subframe shared by multiple users through a dual-antenna transmission scheme by using space-time coding. A first and a second plurality of modulation symbols are generated. A third and a fourth plurality of modulation symbols are generated by performing Alamouti coding on each pair of modulation symbols in each of the first and second pluralities of modulation symbols. A spread matrix is generated for each modulation symbol such that the first and third pluralities of modulation symbols are mapped to a first slot of the subframe, and the second and third pluralities of modulation symbols are mapped to a second slot of the subframe. The subframe is transmitted such that the first and second pluralities of modulation symbols are transmitted via a first antenna, and the third and fourth pluralities of modulation symbols are transmitted via a second antenna.

What is claimed is: 
     
       1. A method in a user equipment (UE) for dual-antenna transmission of a subframe shared by a plurality of users using space-time coding, the method comprising:
 generating, at the UE, a first plurality of modulation symbols and a second plurality of modulation symbols to be transmitted on the subframe; 
 generating, at the UE, a third plurality of modulation symbols and a fourth plurality of modulation symbols by performing Alamouti coding on each pair of modulation symbols in each of the first and second pluralities of modulation symbols; 
 generating a spread matrix for each of the pluralities of modulation symbols such that each column of each spread matrix for the first and third pluralities of modulation symbols maps to a corresponding single carrier-frequency division multiple access (SC-FDMA) symbol of a first slot of the subframe, and each column of each spread matrix of the second and fourth pluralities of modulation symbols maps to a corresponding SC-FDMA symbol of a second slot of the subframe; and 
 transmitting the subframe such that the first plurality of modulation symbols are transmitted on the first slot via a first antenna, the second plurality of modulation symbols are transmitted on the second slot via the first antenna, the third plurality of modulation symbols are transmitted on the first slot via the second antenna, and the fourth plurality of modulation symbols are transmitted on the second slot via the second antenna. 
 
     
     
       2. The method of  claim 1 , further comprising performing a discrete Fourier transform (DFT) on each SC-FMDA symbol for each slot of the subframe before transmitting the subframe. 
     
     
       3. The method of  claim 1 , wherein generating a spread matrix for each of the pluralities of modulation symbols comprises:
 spreading each plurality of modulation symbols across SC-FDMA symbols of the corresponding slot according to an assigned spreading code, wherein the assigned spreading code corresponds to the UE. 
 
     
     
       4. The method of  claim 3 , wherein when an SC-FDMA symbol in the second slot is reserved for a sounding reference signal (SRS) such that a spreading factor for the first slot is greater than the a spreading factor for the second slot, the assigned spreading code is shared with another UE according to a time multiplexing scheme. 
     
     
       5. The method of  claim 1 , further comprising permuting the rows within each spread matrix, wherein the columns within each spread matrix are orthogonal. 
     
     
       6. The method of  claim 3 , wherein each assigned spreading code further corresponds to the slot of the subframe. 
     
     
       7. The method of  claim 3 , wherein the spreading factor determines the maximum number of users that can concurrently transmit information on the subframe. 
     
     
       8. The method of  claim 1 , wherein the first plurality of modulation symbols comprises the same information as the second plurality of modulation symbols. 
     
     
       9. The method of  claim 1 , wherein generating a spread matrix for each of the pluralities of modulation symbols comprises:
 allocating each SC-FDMA symbol in each slot to a distinct subset of the corresponding plurality of modulation symbols such that each distinct subset of the first plurality of modulation symbols corresponds to a distinct subset of the third plurality of modulation symbols, each distinct subset of the second plurality of modulation symbols corresponds to a distinct subset of the fourth plurality of modulation symbols, and the corresponding distinct subsets of modulation symbols map to the same SC-FDMA symbol; and 
 spreading each distinct subset of the corresponding plurality of modulation symbols within each allocated SC-FDMA symbol according to an assigned spreading code, 
 wherein each assigned spreading code corresponds to an index of the slot, an index of the SC-FDMA symbol, and the UE. 
 
     
     
       10. The method of  claim 9 , wherein the first plurality of modulation symbols comprises the same information as the second plurality of modulation symbols. 
     
     
       11. An apparatus in a transmitter of a user equipment (UE) for performing dual-antenna transmission of a subframe shared by a plurality of users using space-time coding, the apparatus comprising:
 a channel coding and modulation block configured to generate a first plurality of modulation symbols and a second plurality of modulation symbols to be transmitted on the subframe; and 
 a transmit diversity processing block configured to:
 generate a third plurality of modulation symbols and a fourth plurality of modulation symbols by performing Alamouti coding on each pair of modulation symbols in each of the first and second pluralities of modulation symbols, and 
 generate a spread matrix for each of the pluralities of modulation symbols such that each column of each spread matrix for the first and third pluralities of modulation symbols maps to a corresponding single carrier-frequency division multiple access (SC-FDMA) symbol of a first slot of the subframe, and each column of each spread matrix of the second and fourth pluralities of modulation symbols maps to a corresponding SC-FDMA symbol of a second slot of the subframe, and 
 
 wherein the transmitter is configured to transmit the subframe such that the first plurality of modulation symbols are transmitted on the first slot via a first antenna, the second plurality of modulation symbols are transmitted on the second slot via the first antenna, the third plurality of modulation symbols are transmitted on the first slot via the second antenna, and the fourth plurality of modulation symbols are transmitted on the second slot via the second antenna. 
 
     
     
       12. The apparatus of  claim 11 , wherein the transmit diversity processing block is further configured to perform a discrete Fourier transform (DFT) on each SC-FMDA symbol for each slot of the subframe. 
     
     
       13. The apparatus of  claim 11 , wherein the transmit diversity processing block is further configured to, when generating a spread matrix for each of the pluralities of modulation symbols, spread each plurality of modulation symbols across SC-FDMA symbols of the corresponding slot according to an assigned spreading code, wherein the assigned spreading code corresponds to the UE. 
     
     
       14. The apparatus of  claim 13 , when an SC-FDMA symbol in the second slot is reserved for a sounding reference signal (SRS) such that a spreading factor for the first slot is greater than the a spreading factor for the second slot, the assigned spreading code is with another user according to a time multiplexing scheme. 
     
     
       15. The apparatus of  claim 11 , wherein the transmit diversity processing block is further configured to permute the rows within each spread matrix, wherein the columns within the each spread matrix are orthogonal. 
     
     
       16. The apparatus of  claim 13 , wherein each assigned spreading code further corresponds to an index of the slot. 
     
     
       17. The apparatus of  claim 13 , wherein the spreading factor determines the maximum number of users that can concurrently transmit information on the subframe. 
     
     
       18. The apparatus of  claim 11 , wherein the first plurality of modulation symbols comprises the same information as the second plurality of modulation symbols. 
     
     
       19. The apparatus of  claim 11 , wherein the transmit diversity processing block is further configured to, when generating a spread matrix for each of the pluralities of modulation symbols:
 allocate each SC-FDMA symbol in each slot to a distinct subset of the corresponding plurality of modulation symbols such that each distinct subset of the first plurality of modulation symbols corresponds to a distinct subset of the third plurality of modulation symbols, each distinct subset of the second plurality of modulation symbols corresponds to a distinct subset of the fourth plurality of modulation symbols, and the corresponding distinct subsets of modulation symbols map to the same SC-FDMA symbol, and 
 spread each distinct subset of the corresponding plurality of modulation symbols within each allocated SC-FDMA symbol according to an assigned spreading code, 
 wherein each assigned spreading code corresponds to an index of the slot, an index of the SC-FDMA symbol, and the UE. 
 
     
     
       20. The apparatus of  claim 19 , wherein the first plurality of modulation symbols comprises the same information as the second plurality of modulation symbols.